What Is Jet Aeration?
It can also be used for mixing and agitation, for example in equalization tanks, buffering tanks, selector tanks, rapid-mix tanks, flocculation tanks, neutralization tanks, chemical oxidation tanks, disinfection tanks, sludge storage tanks, denitrification tanks and chemical reaction tanks, as well as for agitation in air-lift and heat exchange systems.
A jet aeration system consists of three parts: the jet aerator, the circulation water pump and the blower.
The power fluid passes through the aerator's guide ring into the power nozzle, forming a high-speed fluid. Due to the entrainment effect of the jet, air is drawn in at the air suction port. The entrained air expands rapidly, and the expanding air is sheared by the high-speed power fluid into tiny bubbles. The bubbles are carried by the power fluid into the mixing chamber, where gas, water and sludge mix thoroughly; the mixed gas-liquid-solid mixture then enters the diffusion chamber, where kinetic energy is gradually converted into potential energy, and the mixture is ejected at high speed against the outlet back pressure.
With jet aeration, the oxygenation efficiency increases as water depth increases. A new-generation jet aerator can reach 35% oxygenation efficiency at a water depth of 8 meters, with an air-to-water ratio of only 4:1. Less water is used to transfer the same amount of air, energy consumption decreases accordingly, and wastewater treatment costs are greatly reduced.
The gas is impacted and sheared by the high-speed fluid into extremely fine bubbles — one of the reasons for the high oxygen utilization. The turbulence generated by the jet aerator continuously renews the gas/liquid contact surface, which also favors oxygen transfer.
The oxygen utilization measured for each aeration method when aerating oxygen-free clean water at 20 degrees Celsius and one atmosphere is the SOTR (Standard Oxygen Transfer Rate). In actual aeration of wastewater, the large amounts of salts, COD and SS contained in the sewage cause the actual oxygen utilization to decrease to a greater or lesser extent; the alpha coefficient is the parameter characterizing the magnitude of this decrease. For a given wastewater, the alpha coefficient depends on the aeration device, and alpha is defined as the ratio of the oxygen utilization of a given aeration device in the given wastewater to that in clean water. Fine-bubble diffusers generally have an alpha coefficient of about 0.4, while jet aeration has an alpha coefficient as high as 0.95, mainly thanks to the powerful jet, which gives the gas the energy to overcome the surface tension of the sewage, making it easier for the gas to overcome the resistance of gas/liquid phase transfer.
The oxygenation and mixing of the jet aerator can be controlled independently. Operators can adjust the air volume according to dissolved oxygen demand, while mixing is achieved by the circulating water. Combined with manual control and automatic DO-meter control, the air supply can be turned down at low loads to effectively reduce energy consumption while maintaining the system's capacity to meet the load. Maintaining the mixing state even when the air supply is stopped makes it highly suitable for anaerobic/aerobic alternating cyclic biochemical treatment systems (such as SBR and CASS).
Thanks to its materials and structure, the jet aeration system is sturdy, wear-resistant and corrosion-resistant; under normal use and maintenance conditions, its design service life is generally 10-15 years.
The jet aerator has high oxygen utilization and is installed at the bottom of the water, so it does not produce water mist and foam the way surface aeration equipment (surface aerators, brush aerators) does.
Because the jet aeration system works on a principle and has structural features completely different from traditional aeration methods such as fine-bubble aeration, its high-strength jet main pipeline and highly wear-resistant nozzles give it extremely low maintenance requirements. The PP material used has excellent corrosion resistance, effectively avoiding breakage, detachment, corrosion and wear, and there are no moving parts in the tank, greatly reducing the failure rate. However, the normal operation of the jet aeration system still requires periodic inspection of pipes and valves, cleaning of nozzles to prevent clogging, and routine maintenance of auxiliary equipment such as the circulation pump and blower. In service environments with high hardness, high salinity and high COD, which often cause clogging and damage in fine-bubble aeration and other methods, the narrowest part of the jet aeration system is the nozzle, and this is where the high-speed jet occurs; the intense scouring action makes scaling and crystallization difficult to form.
The auxiliary equipment of the jet aeration system refers to the circulation pump and the blower; all rotating parts are located outside the tank, making repair and maintenance very convenient without emptying the tank.
The jet aeration system achieves thorough mixing without covering the entire tank bottom, which can significantly save installation time and installation costs.
